Figure 4: Actuation mechanism via solvent molecule sorption.

(a) A scheme of the porous membrane actuator (left, not to scale), definition of variables: h, thickness of the membrane; r, radius of the bended membrane arch; D, thickness of the pore wall; A, the diffusion track of acetone molecules from outside to the surface of pore walls inside the membrane; (top right) chemical structure of the ‘imidazolium~Tf₂N’ pair; (lower right) the representative snapshot of solvent redistribution around the ‘imidazolium ~ Tf₂N’ ion pair: water molecules (blue) are partially displaced by acetone molecules (red), which adsorb more to the Tf₂N anion on the left of the snapshot. (b) Curvatures of PILTf₂N/C-pillar[5]arene membrane actuator in vapour of different solvents (2 kPa, 20 °C). (c) Effect of PF₆ anion content on curvature of PIL(Tf₂N+PF₆)/C-pillar[5]arene membrane actuator in 3 mol% acetonitrile–water and 3 mol% acetone–water mixture, respectively.